A series of alkylazulene-1-sodium sulfonate derivatives which has an isopropyl group at 6-position were synthesized, and their anti-ulcer activities were examined in Shay pylorus-ligated rats. The values of lipophilicity (log P) as a parameter of these new azulene derivatives were also examined in reference to the structure-activity relationship. The optimum value of log P, which showed maximal anti-ulcer activity, was about -0.46. Among the derivatives of azulene examined, 3-ethyl-6-isopropylazulene-1-sodium sulfonate (compound IXb:XT1-785) exhibited the most potent inhibitory action against Shay ulcer, and its anti-peptic activity was similar to that of 3-ethyl-7-isopropylazulene-1-sodium sulfonate (KT1-32). It also had more activity than guaiazulene sodium sulfonate (GAS). Furthermore, KT1-785 was extremely stable under heating as compared to GAS.